This invention relates to connecting means for mounting and electrically connecting leadless circuit boards such as leadless integrated circuit packages, leadless large scaled integrated circuit packages, and leadless printed circuit boards to other circuit boards, and in particular, to contact elements used for such electical connection.
In order to electrically connect the leadless circuit boards (which will be referred to as "daugher board") employing terminal pads in place of leads onto another circuit board (which will be referred to as "mother board") such as a printed circuit board and a wiring board, an electrical connector has been used in the prior art as disclosed in U.S. Pat. Nos. 3,904,262, 4,063,791, 4,204,722 and others. Generally speaking, such a connector includes a housing of insulator material for receiving the daughter board therein, a plurality of contact element fixedly mounted in the housing to engage with terminal pads of the daughter board and to connect with conductor elements of the mother board on which the connector is mounted.
In conventional connectors of such a type, it has been desired to clamp the daughter board and the connector housing, to thereby maintain press contact of the terminal pads of the daughter board with the contact elements. A known clamping means has a cover plate to be engaged with the upper surface of the daughter board received in the housing and screw members for fastening the cover plate to the housing, for example, at four corners of the housing. In such a clamping means, the cover plate receives an upward force through the daughter board due to a reaction force of the contact elements, and therefore, the upward force acts on the housing through the screw members. Therefore, the cover plate and the housing are deflected, especially at intermediate portion between two screw members is greatest. As a result, the intended contact force cannot be obtained between certain pads and the corresponding contact elements.
Furthermore, in use for a long time and/or under a high temperature, the cover plate and the housing are permanently deformed because of deterioration of their insulator materials such as plastic resin, so that reliable contact between the pads and the contacts cannot be insured.